Microstrip antennas and their histories are described in the "Proceedings of the IEEE", Volume 80, No. 1, January 1992. The basic configuration of the microstrip antenna is a metallic conductor, such as a patch printed on a thin, grounded, dielectric substrate. This element can be fed either with a coaxial line through the bottom of the substrate or by a co-planar microstrip line. A microstrip antenna radiates a relatively broad beam broadside to the plane of the substrate.
Because of the skin effect, currents in a microstrip antenna flow mainly in the outer and inner surfaces of the conductor, for example the patch. The inner surface of the patch adjacent the dielectric substrate, faces the ground plane. Accordingly, the current on the inner surface is substantially higher than the current on the outer surface. However, it is mainly the outer surface which radiates or receives radiation. Currents on the inner surface are incapable of producing radiation because the conductive portion of the patch between the outer and inner surface blocks radiation which the current at the inner surface may generate. This limits the efficiency of the radiation.
An object of the invention is to improve microstrip antennas.